The invention concerns a value-bearing document with a carrier comprising a paper material and a laminating film which is applied to the carrier and which has a carrier film and a decorative layer having one or more optical security features, as well as a process for the production of such a value-bearing document.
In order to enhance the forgery-proof nature of value-bearing documents it is known for example to apply to bank notes or visas a hot stamping film with an optical security feature. When hot stamping films are applied to value-bearing documents, it is only the transfer layer of the hot stamping film but not the carrier film that is transferred. As the layer array of the transfer layer is typically between 6 and 12 μm in thickness the application operation can be effected at comparatively low temperatures and pressures. That means that only low thermal stresses occur during the hot stamping operation and upon cooling after the stamping operation has been implemented so that at best minimum deformation of the composite comprising the value-bearing document and the layer array occurs. The thermal stresses of the composite comprising the value-bearing document and the layer array of the transfer layer can be further minimized by suitably implementing the properties of the transferred layers.
The transfer layer is typically made up of lacquer, adhesive and metallic layers which are of entirely different physical properties (thermal conductivity, thermal capacity, thermal expansion and so forth) from the carrier.
The small thickness of the transferred layer array and the low inherent stability thereof makes it almost impossible to subsequently detach the applied transfer layer of the hot stamping film from the value-bearing document, without entailing destruction. That means that the production of forged documents by removal of the transfer layer of the hot stamping film from the original document and applying the detached layer array to forged documents is extremely difficult.
It is further known for optical security features to be applied to bank notes using laminating films. In contrast to hot stamping films, in the film body which is transferred onto the bank note laminating films have a carrier film which for example comprises a polyester film of a thickness of between 19 μm and 50 μm and imparts a certain level of inherent mechanical stability to the laminating film. Thus EP 0 723 501 B1 discloses forming an opening in the paper carrier of a bank note and closing that opening again by means of a cover film which is at least region-wise transparent. In that case the cover film comprises a laminating film which includes a transparent carrier film and a decorative layer which adheres firmly to the transparent carrier film. In that arrangement the decorative layer has a lacquer layer which is transparent at least region-wise at least in the region of the opening. In that case diffraction structures which have an optical-diffraction effect and which afford an optical security feature are shaped into the lacquer layer.
Applying laminating films to value-bearing documents makes it possible for a plurality of security features to be transferred during one application operation and for additional functionalities to be transferred onto documents by means of stamping processes. Advantages are afforded in particular in the production of value-bearing documents with windows, but also in the production of value-bearing documents with electrical functionalities, for example documents with integrated circuits, antennas and displays. Laminating films are more suitable for that use than hot stamping films as, by virtue of the mechanical stability of the carrier film, on the one hand they ensure better processability in the application operation while on the other hand they ensure stabilization of the layer array on the document after application. The carrier film of the laminating film also represents protection from environmental influences and from attempts at manipulation.
However substantially higher temperatures and pressures are required when applying laminating films to paper substrates, than for applying hot stamping films. The differing thermal coefficients of expansion of the film and the substrate as well as the heating thereof to differing extents mean that, when cooling occurs, high thermal stresses are induced, which can result in distortion of the film-substrate composite, whereby flat positioning of the value-bearing documents may no longer be possible and further handling and processability, for example when stacking sheets, can be made difficult.
It is further known from EP 0 748 286 B1 for a perforated pattern to be introduced by means of a laser beam into the carrier of a check, a bank note or a credit card which is provided with an individualized pattern printed thereon, for example a serial number. The printed individualized pattern can be perceived with the human eye just like the individualized pattern formed from perforations. The perforated pattern and the printed pattern have the same characters so that forgeries can be easily detected. In that case forgery of the value-bearing document is particularly difficult as it is almost impossible for the resulting perforations to be filled up.